The present invention relates generally to apparatus for heating components, and more particularly, to optical heat-generating apparatus and methods for use in shrinking heat shrinkable tubing, fusing insulated wires together, and solder and unsolder packaged IC chips.
The assignee of the present invention manufactures switching devices having wires or harnesses extending therefrom that require insulation. Typically, heat shrink tubing is placed over exposed wires and is heated so that it shrinks to closely fit around the wires.
Prior art apparatus for heating heat-shrinkable tubes is disclosed in U.S. Pat. No. 4,460,820 issued to Matsumoto, et al. The apparatus comprises a supporting unit for a heat-shrinkable tube and a plurality of heating units that are disposed in the longitudinal direction of the heat-shrinkable tube. The heating units comprise electric heaters that can be operated independently.
U.S. Pat. No. 5,060,289 issued to Abramson discloses a portable tube shrinking tool. The tool comprises a heating device that includes a pair of facing concave surfaces for directing radiant energy toward an object to be heated positioned in a receiving space between the concave surfaces. The radiant energy is produced by two pluralities of radiant heating lamps, each of which is located between the receiving space and a corresponding concave surface. The lamps and concave surfaces are contained within an enclosure that has an access opening to the receiving space, and with each concave surface substantially extending to that opening.
Furthermore Eraser Company Inc. of Syracuse N.Y., manufactures a variety of glow-ring type heating devices for use in shrinking heat shrinkable tubing. Quartz encapsulated heating elements are used that open and close in the manner of a thumb and forefinger to encircle workpieces that are heated by the heating elements.
Conventional approaches for shrinking the heat shrinkable tubing around the wires were tried but found inefficient or impractical for a high volume manufacturing environment. For example, hot air and infrared heat conveyor ovens were evaluated for use, but were found unsuitable. It was determined that all components attached to the wiring harness would have been exposed to heat, which is not desirable.
Hot air guns were initially used on stands attached to work benches on production lines to shrink the heat shrinkable tubing. The heat gun approach resulted in slow operation. It was also found that the tubing was not straight after shrinking. Additionally, the harness often times got tangled. From a production perspective, there was too much human handling of the wiring harness. The heat guns also had other disadvantages including power usage, heat, noise, and maintenance problems.
Heat delivery is highly dependent on distance from and alignment with the nozzle of the heat gun, and rotating the tubing is desirable for even shrinking. Shrinking more than a nozzle width of tubing (typically about 2 inches) is particularly slow and demanding. While hot air guns are well suited for occasional use, in a production environment they require too much mental concentration, and quality control problems can result.
Ellipsoid (surface of rotation, not extrusion) reflectors, that focus light located in one focal point at the other focal point, are old art. While only half of the ellipsoid surface is typically used, it captures about 80% of the energy and delivers it to about xe2x85x9 of the target surface. A full ellipsoidal surface entirely enclosing both the source and the target, delivers the light to the target in a cardoid pattern. Most of the light strikes the target from the direction of the source and nothing comes from the opposite direction where the target casts a shadow on the reflector.
The directionality of the cardoid pattern produced by such a full ellipsoidal reflector is such that typically about ⅚ of the radiant energy is delivered to the target half facing the source and ⅙ to the back half. Such uneven energy delivery scorches the tubing on one side while leaving the other side cold.
In view of the above, it is an objective of the present invention to provide for improved optical heat-generating apparatus and methods for use in shrinking heat shrinkable tubing and fuse insulated wires together.
To accomplish the above and other objectives, the present invention provides for optical heat-generating apparatus and methods that rapidly, controllably deliver energy (heat) to heat shrink tubing disposed over wires or other components and that may be used to fuse insulated wires together. A number of different embodiments of the apparatus have been developed. In times of from less than 1 second up to 3 seconds, lengths of heat shrink tubing have been shrunk ranging between 3 to 20 inches, although there are no specific length limitations on the apparatus.
In general, the optical heat-generating apparatus comprises a housing having one or more reflective cavities that each comprise a linear elliptical reflective surface having first and second focal lines, and into which the heatable component is inserted and disposed along the first focal line. One or more optical heat-generating elements are disposed along the second focal line of each respective linear elliptical reflective surface that emit energy that is focused by the one or more linear elliptical reflective surfaces onto the heatable component disposed along the first focal line.
An exemplary optical heat-generating apparatus comprises a modular heater having two quartz-halogen lamps with straight coil filaments. To deliver heat evenly to the tubing from all directions (360 degrees around the longitudinal axis of the tubing) a double linear elliptical reflector module, about as long as the lighted filament, is disposed around the lamps. At each end of the reflector, a thin plate with polished reflective surfaces helps position the tubing at a common focal point of both ellipses, while the filaments are held at the outer focal point of each reflector.
The optical heat-generating apparatus is preferably maintained at a partial heat level between power applications, to reduce reaction time. This also reduces thermal shock to the filaments, extending bulb life. A foot-switch or button actuated timer may also be used to control power on-time for consistent quality.
Double lobed linear elliptical, and triple lobed linear elliptical reflectors were evaluated for use in the present invention. It was determined that the double lobe design was preferred, but three or more lobes might be desirable in specific applications. For most applications, the double lobe design offers well-balanced circumferential heat delivery, simplicity of construction use, cooling (a factor in continuous assembly line use) and service.
Some embodiments of the apparatus have a modular construction, where shrink length is not limited by filament length. One embodiment uses one lamp per shrunk length, where the lamp ends and terminations alternate on each side of the of the tube.
Another embodiment provides circumferential heat delivery by employing two different elliptical reflectors sharing the source focal line. One reflector, however, redirects about half of the light to a phantom focal point, thus missing the target. A flat reflector reflects this light into the target from behind, evening out power delivery.
Another embodiment uses staggered dual reflectors that are angularly rotated around an axis relative to the target, and uses relatively small (2xc2xe inch long) lamp segments. Yet another embodiment uses a string of small lamps in dual elliptical reflectors, each in a socket, offering essentially any heat zone length, from a few thousands of an inch to many feet.
Means for limiting heat delivery to specific areas by masking, preferably with reflective surfaces, may be built into the apparatus, or pre-applied to the part before insertion into the apparatus. Heat absorption is color dependent, and in many applications, color (either a colored material or an applied paint) may be used to help or hinder heating of specific parts.
Heat shrink tubing is widely used in many different applications. In terms of location and accessibility at the shrink operation, most fall into one of two categories: xe2x80x9cjacketxe2x80x9d and xe2x80x9cterminationxe2x80x9d. The apparatus that have been reduced to practice, satisfies the xe2x80x9cjacketxe2x80x9d need, where the shrinkable tubing is disposed over a length of wire or similar long, slender object, and one or both ends emerge from the tube and are available to position the tube for the shrinking operation.
The xe2x80x9cterminationxe2x80x9d application has limited accessibility, and typically one or more wires or the like are next to a bulky object such as a connector or bulkhead. One embodiment of the present invention allows all the bulky components (lamp and main reflectors) to be off to one side, with only the rear mirror behind the shrinkable tubing. This permits fairly even delivery of energy to the heat shrink tubing.
An exemplary method of shrinking heat shrinkable tubing is as follows. One or more reflective cavities are provided that each comprise a linear elliptical reflective surface having first and second focal lines. One or more optical heat-generating elements are disposed along the second focal line of each respective linear elliptical reflective surface. A heatable component is disposed along the first focal line. Energy emitted by the optical heat-generating elements is focused by the one or more linear elliptical reflective surfaces onto the heatable component disposed along the first focal line.
An exemplary method of fusing insulated wires together is as follows. One or more reflective cavities are provided that each comprise a linear elliptical reflective surface having first and second focal lines. One or more optical heat-generating elements are disposed along the second focal line of each respective linear elliptical reflective surface. Insulated wires that are to be fused together are disposed along the first focal line. The energy emitted by the optical heat-generating elements is focused by the one or more linear elliptical reflective surfaces onto insulation of the insulated wires to fuse them together.
Another aspect of the present invention provides for two adjacent linear elliptical reflective surfaces, each having first and second focal lines, where the second focal lines are coincident. Heatable components are disposed along the two first focal lines. This embodiment may be used to solder or unsolder electronic components having multiple leads arranged in two parallel lines, such as dual inline packaged semiconductor chips.